Nowadays, magnetic elements such as inductors and transformers are widely used in many electronic devices to generate induced magnetic fluxes. Recently, since the electronic devices are developed toward minimization, the electronic components contained in the electronic products become small in size and light in weight. Therefore, the magnetic element and its conductive winding module are slim.
Take a transformer for example. FIG. 1A is a schematic exploded view of a conventional transformer. The transformer 1 comprises a bobbin 11, a magnetic core assembly 12 and a coil 13. The bobbin 11 has a winding section 111 for winding the coil 13 thereon. The bobbin 11 further has a channel 112 running through a center portion thereof. In addition, the bobbin 11 has several pins 113 extended from the bottom surface thereof and connected to the coil 13. By soldering the pins 113 on a circuit board (not shown), the transformer 1 is mounted on and electrically connected to the circuit board. The magnetic core assembly 12 includes a first magnetic part 121 and a second magnetic part 122. The first magnetic part 121 has a middle post 121a and two lateral posts 121b. The second magnetic part 122 also has a middle post 122a and two lateral posts 122b. As such, the first magnetic part 121 and the second magnetic part 122 of the magnetic core assembly 12 are cooperatively formed as an EE-type core assembly.
For assembling the transformer 1, the middle post 121a of the first magnetic part 121 and the middle post 122a of the second magnetic part 122 are aligned with and embedded into the channel 112. In addition, the lateral posts 121b of the first magnetic part 121 are contacted with the lateral posts 122b of the second magnetic part 122. As such, the coils 13 will interact with the magnetic core assembly 12 to achieve the purpose of voltage regulation. The resulting structure of the assembled transformer 1 is schematically shown in FIG. 1B.
When the conventional transformer 1 is applied to a power factor correction (PFC) circuit, the distance between the middle post 121a of the first magnetic part 121 and the middle post 122a of the second magnetic part 122 should be adjusted such that the air gap of the transformer 1 is changed. As the air gap of the transformer 1 is changed, the inductance of the transformer 1 could be controlled.
For achieving the purpose, portions of the middle posts 121a and 122a are scraped by a tool such that middle post 121a/122a is shorter than the lateral post 122a/122b by d0 (as shown in FIG. 1A). Under this circumstance, after the middle post 121a of the first magnetic part 121 and the middle post 122a of the second magnetic part 122 are embedded into the channel 112, the middle post 121a is distant from the middle post 122a by an air gap of 2×d0. Due to the air gap, the inductance of the transformer 1 is adjusted.
The process of fabricating the transformer 1 has some drawbacks. For example, since the lateral posts 122a and 122b are disposed at bilateral sides of the middle posts 121a and 122a, the lateral posts 122a and 122b become hindrance from scraping the middle posts 121a and 122a. Especially when a longer air gap is required, the process of scraping the middle posts 121a and 122a is time consuming and complicated.
Moreover, the air gap of the conventional transformer 1 is fixed. For changing the air gap of the transformer 1, a new magnetic core assembly is provided and portions of the middle posts 121a and 122a are scraped. In other words, the original magnetic parts 121 and 122 will be discarded and thus the fabricating cost is increased. In addition, discarding the original magnetic parts 121 and 122 is not environmentally-friendly. The process of scraping the magnetic core assembly results in much core powder, which also incurs pollution. Since the magnetic core assembly is usually scraped by a grinding wheel, the internal portion of the magnetic core assembly is possibly damaged to some extents and the performance of the transformer 1 is deteriorated.
Since the middle post 121a is distant from the middle post 122a by an air gap of 2×d0, an edge effect is generated. Under this circumstance, the eddy loss is increased, and the operating temperature of the transformer 1 is increased. An additional heat-dissipating mechanism increases the overall cost.
Therefore, there is a need of providing an improved transformer so as to obviate the drawbacks encountered from the prior art.